2000 Big Bear won't start backfires

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  #1  
Old 07-11-08, 07:33 AM
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2000 Big Bear won't start backfires

Hi,
I have a 2000 Big Bear 400. I bought it last winter. The guy had just bought a new battery and we put it in and started it. At the time it was freezing cold.. say 15-20 degrees. I took it home and started it a couple more times. It would run a few minutes and quit. It acted like it was loading up. When I bought it there was gas in the airbox. We put more gas in it and the airbox filled up even more. When I went to check the oil the chamber was also full of gas. Anyway I drained the tank, the oil, took the carberator apart cleaned it and put it back on. I filled it with oil and gas and put a fuel filter between the gas tank and the carberator. The airbox no longer fills with gas and the crankcase still it just oil. It is summer now and I am trying to get this running and can't get it started. I switched the carberator with the one on my 2000 kodiak 400 and it didn't make a difference. I checked the compression with the throttle open and after cranking a few times the compression is 124psi. I choke it and crank it and it will consistently backfire. Sometimes it is just little pops sometime it sounds like a shotgun. I pulled the spark plug out and it looks like it is getting good spark. I checked the resistance on the stator wires and get about .8 ohms between each. With the stator disconnected from the three wire plug it backfires just the same. I tried to use starting fluid and it doesn't help it still backfires. I am getting very frustrated and hope one of you smart people out there can help me figure this thing out... Thanks very much in advance...
 
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  #2  
Old 07-11-08, 09:25 AM
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switched cdi boxes same old same old

I switched cdi box with my 2000 kodiak 400. Still backfires the same way. I did see fire shoot almost to the ground from the exhaust pipe, this happens sometimes.
 
  #3  
Old 07-11-08, 09:34 AM
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One more thing..

It spits air back through the carb sometimes in addition to backfiring.
 
  #4  
Old 07-11-08, 10:00 AM
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Timing

I tried to check the timing with a light while cranking but there is too much oil splashing out of the hole to see the marks.
 
  #5  
Old 07-11-08, 11:34 AM
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When you had gas in everything , that would have been the float valve. Sounds like you got that taken care.

A flooded condition takes a little work to get out of though. Your carb may or may not be just right.

I would make sure your air flow routes are clear = intake and exhaust. Then take the fuel out of the carb = drain the bowl and shut off the fuel from the tank. Then purge everything out of the engine by removing the spark plug, full throttle, no choke, and spin the engine over about ten to fifteen times. Then spoon a teaspoon of gas down the plug hole, spin the engine a couple of times over - no more. This pretty well takes the carburetor out of the equation.

Then put the plug back in and see if it tries to start. If it does, turn the fuel on at the tank for about five seconds and shut it back off. Then see if the engine will start and run for a short time. If it does, post back - the carb needs some attention.
 
  #6  
Old 07-12-08, 07:04 PM
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Wow!

When the air is cold, it is denser and needs a richer mixture. It'll backfire and run rough in the cold. Those of us without fuel injection just leave the choke on a little bit in the winter. This keeps the engine from overheating under extreme cold conditions (sounds weird, but it's true). You need a richer mixture when cold.. That's probably why it worked in the dead of winter.

There is an outside chance the Intake valve is misadjusted. I learned the hard way to adjust older Suzuki Valves when the engine is cold. Adjust warm and it won't start up the next day. I've never had this temperature problem with Yamaha or Honda... but you never know when something temperature sensitive will bite you.

I'm thinking your intake valve never shuts.
 

Last edited by wobweeder; 07-12-08 at 08:26 PM.
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